Heretofore, methods of spraying a quick-setting concrete obtained by mixing a concrete with a powder is quick-setting admixture were employed to prevent break and fall of ground exposed in excavation works of tunnels or the like (cf. Patent Document 1 and 2).
As the quick-setting admixture for such spraying methods, one having an alkali metal aluminate, an alkali metal carbonate or the like admixed with calcium aluminate was used, as it was excellent in the quick-setting property.
However, there has been an increasing demand for a quick-setting admixture having a pH-value lower than that of the quick-setting admixture having an alkali metal aluminate, an alkali metal carbonate or the like admixed with calcium aluminate, and being weakly alkaline to acidic, preferably neutral or weakly acidic.
Further, as a tool to add the quick-setting admixture to concrete, it was common to use a Y-tube. In such a case, in order to increase the mixing efficiency, it was common to employ a method wherein concrete was once disintegrated by means of compressed air and then the quick-setting admixture was added. As a result, the amount of compressed air to be used for spraying tended to increase, and the amount of dust formed tended to increase sometimes. Accordingly, at the time of spraying, it was necessary to take some measure to cope with such dust.
In order to solve such problems, as a liquid quick-setting admixture, one containing a basic aluminum salt or an organic carboxylic acid as the main component (Patent Document 3), one containing aluminum sulfate or an alkanolamine as the main component (Patent Document 4), or one containing a basic aqueous solution of aluminum, and lithium silicate and lithium aluminate as the main components (Patent Document 5) was, for example, used.
However, with this liquid quick-setting admixture, the initial strength was hardly obtainable, and as compared with a conventional powder quick-setting admixture, there was a danger of falling when sprayed thickly in a tunnel.
In order to solve such problems, a technique was developed to mix water to a quick-setting admixture comprising calcium aluminate and aluminum sulfate to form a slurry, which was added to concrete (Patent Documents 6, 7 and 8).
This technique is to reduce a damage by alkali reagents by a combined use of aluminum sulfate and calcium aluminate. Further, it is a technique to attain a low dusting property by mixing the powder quick-setting admixture with water to form a slurry. Further, these patent documents describe about an AE agent and a blowing agent, but they are mentioned as substances to reduce the amount of dust by adding them preliminarily to concrete, and there is no mention about using a blowing agent in a quick-setting admixture.
As a tool to add such a slurry quick-setting admixture to concrete, a Y-tube or a showering ring to add a quick-setting admixture in the form of a shower into a concrete piping, was, for example, used.
In the case of the Y-tube, in order to improve the mixing property, a technique was used to once disintegrate concrete by means of compressed air and then add the quick-setting admixture, and as a result, the amount of compressed air used for spraying tended to increase, and the amount of dust formed tended to increase sometimes.
On the other hand, in a case where the showering tube is used, the mixing property of the slurry quick-setting admixture and concrete will be good, whereby low dust spraying will be possible without requiring air for disintegration. On the other hand, the structure is complicated, and the frequency of solidification of the slurry inside was more than the case of Y-tube, whereby the showering tube was not practically useful.
Accordingly, in spraying by means of a showering tube, a liquid quick-setting admixture is mainly used, but the components of a liquid quick-setting admixture are only components to accelerate a hydration reaction of cement and do not have a self-curing property whereby they are cured by themselves to impart a quick-setting property. Thus, there was a problem that it was inferior in the quick-setting property as compared with a slurry quick-setting admixture containing calcium aluminate.
As a liquid quick-setting admixture having the quick-setting property more improved than ever, one having a fluorine element incorporated to aluminum sulfate was developed (Patent Documents 9, 10 and 11).
However, for practical application, further improvement of the quick-setting property, improvement of the adhesive property at a spring water area, etc. have been desired.
Further, a technique for combining a liquid quick-setting admixture and a powder quick-setting admixture has also been published (Patent Documents 12 and 13). However, in a case where at the time of spraying, a liquid quick-setting admixture and a powder quick-setting admixture are mixed to form a slurry, there has been a case where the slurry undergoes solidification in the same manner as the above-mentioned slurry quick-setting admixture. Accordingly, it has been desired that the slurry will not solidify at the portion of the quick-setting admixture-adding tool and that the replacing cycle of such a tool is long.
Further, a technique of adding a liquid quick-setting admixture comprising aluminum sulfate, a calcium aluminate, a water-reducing agent and water, to cement concrete containing an inorganic powder (Patent Document 14), a technique of adding a liquid quick-setting admixture to concrete employing cement containing calcium carbonate (Patent Document 15) and a technique of incorporating calcium carbonate to a cement composition and using a liquid quick-setting admixture in combination therewith (Patent Documents 16, 17 and 18) have been published. However, in these techniques due to alkali of the cement component contained in a large amount, calcium carbonate will not be an acidic atmosphere, and the slurry quick-setting admixture tends to form bubbles, and they are neither techniques to prevent solidification nor techniques to obtain a low dusting property by means of a showering tube.
Further, with a mixture having a quick-setting admixture preliminarily incorporated to a cement composition, it is not possible to obtain a fluidity retention of concrete. Accordingly, it was necessary to mix immediately before spraying, an aggregate, a cement composition and a liquid quick-setting admixture, and there was a problem such that a spraying concrete having a uniform composition was hardly obtainable. Further, no mention was made with respect to the effectiveness of an alkali metal sulfate in a quick-setting admixture wherein an acidic substance and a blowing agent are used in combination.
In recent years, it has been desired to develop a quick-setting admixture which is less influential to a human body as compared with a conventional basic quick-setting admixture, which is excellent in providing initial strength and which is scarcely solidified at the portion of the quick-setting admixture-adding tool.
Patent Document 1: JP-B-60-004149
Patent Document 2: JP-A-09-019910
Patent Document 3: JP-A-2001-509124
Patent Document 4: JP-A-10-087358
Patent Document 5: JP-A-2001-130935
Patent Document 6: JP-A-2000-302505
Patent Document 7: JP-A-2000-302506
Patent Document 8: JP-A-2001-302323
Patent Document 9: JP-A-2002-080250
Patent Document 10: JP-A-2002-047048
Patent Document 11: JP-A-2004-035387
Patent Document 12: JP-A-2002-220270
Patent Document 13: WO2005/019131
Patent Document 14: JP-A-2001-270768
Patent Document 15: JP-A-2003-321263
Patent Document 16: JP-A-11-79818
Patent Document 17: JP-A-2001-270768
Patent Document 18: JP-A-2007-119263